PET-CT examination precautions: First, need to fast, this is the issue we must emphasize, before the examination should be fasted 4-6 hours, at least 4 hours, otherwise the fasting time is not enough, it will affect the quality of PET-CT image. Because malignant tumors will be highly ingested, but there are some normal tissues in human body, which will also absorb the drug, we call it background-like absorption, for example, the brain will absorb deoxyglucose, and then the performance in the brain is high density, such as stomach and intestine, we call it physiological uptake; secondly, before the examination, we should rest and cannot move around, for example, patients walk or run to the hospital and inject the drug immediately, after PET-CT Thirdly, after the injection of drugs, it is recommended that the patient should rest quietly for another hour, during which time he should not make any movements and keep the metabolic level low in his body, so that the PET-CT images made will be qualified and will not affect the diagnosis, otherwise various artifacts will appear. It is more troublesome to determine the pathological nature of the tumor, so the preparation of the patient before the examination is crucial.